1. Field of the Invention
The present invention relates to a valve operating control system for an internal combustion engine, including a cam change-type valve operating characteristic changing mechanism, and a control unit for controlling the valve operating characteristic changing mechanism in a feedback manner and in a feed-forward manner.
2. Description of the Prior Art
Internal combustion engines, which include a cam phase changing-type valve operating characteristic changing mechanism constructed to continuously control the timing of the opening and closing of an intake valve or an exhaust valve, are known from Japanese Patent Application Laid-open No. 59-93964 and Japanese Patent Publication No. 5-43847.
In carrying out the control for converging a deviation between an actual cam phase and a target cam phase to zero in such valve operating characteristic changing mechanism, if the feedback control is carried out when the deviation is large, a responsiveness can be ensured, but there is a possibility that the actual cam phase overshoots the target cam phase, whereby the convergence cannot be ensured. In such a case, it is conceived that while the deviation is large, a feed-forward control is carried out to ensure the convergence, and after the deviation becomes small, feedback control is carried out, thereby enabling the responsiveness and the convergence to be reconciled.
When the feedback control and the feed-forward control are used in combination with each other, the effect can be exhibited in a particular operational state of the internal combustion engine, however, there is a possibility that a sufficient effect cannot be obtained depending on the operational state of the internal combustion engine over a wide range of an operational condition, e.g., the level of the engine temperature.